The present invention relates to a TIG welding method and apparatus suitable for welding a building or structure having a large size such as power plant, particularly, for carrying out an entire welding attitude including vertical and upward welding attitudes of an welding apparatus in a stable manner with high fusing efficiency.
The TIG welding method has been widely utilized, as a well known welding method, for various welding workings requiring high quality of a welded portion because, by the TIG welding, a portion to be welded is shut off from an environment air by a shield gas jetted around an electrode to thereby prevent oxidation and nitriding of that portion. However, since, in such TIG welding method since a non-fusible tungsten electrode is used, the welding efficiency is not good in comparison with an MIG welding method or other method using a fusible electrode. Moreover, in an occasion that a feeding speed of a wire to be fed as a filler material is excessively increased over a limit of welding penetration depth of the wire, there may be caused a case where a portion of the wire which has not been completely melted abuts against a bottom portion (portion not to be welded or solid portion such as previously welded bead) of a molten pool, which will result in an instable welded condition.
In a known art, various efforts have been made for solving the problems mentioned above. For example, there is provided a double-gas-shield method in which inner and outer double gas shields are formed around the tungsten electrode to enhance a thermal pinch effect and hence to create an arc throttled state and increase the welding penetration depth. Examples of TIG welding methods utilizing such double-gas-shield technique are disclosed in Japanese Patent Laid-open Publication No. HEI 6-71446 in which it is attempted to make constant the welding penetration depth through controlling of a gas supply amount and in Japanese Patent Laid-open Publication No. HEI 7-227673 in which it is attempted to increase operational efficiency through an improvement of gas supply density.
In another aspect, further attempts have been made from the view point of a wire to be applied. For example, there has been proposed a method in which a plurality of wires are simultaneously fed to perform deep welding penetration under high voltage or a method in which the welding wire is heated through current conduction to facilitate the fusing of the wire and hence to increase the welding penetration. However, as mentioned, in these prior art methods, the attempts have been carried out only in a view point of increasing the wire welding penetration, and these methods have been carried out separately.
In order to connect or join a large structure such as construction of a large building such as power plant and/or to connect or join a structure having a large thickness such as duct jointing, it is required for the application of the TIG welding to improve welding stability with no welding defect, welding speed, fusing speed of the wire or the like. However, in the welding working site of the construction of the power plant, for example, it is needed to carry out the welding in an entire directional welding attitude or position of a welding apparatus such as normal downward welding attitude, standing vertical welding attitude welding or upward welding attitude. However, in the standing attitude welding or upward attitude welding of the welding apparatus, the surface of the molten pool in the TIG welding is directed horizontally or downward, and accordingly, there may occur a case that a balance of force acting to the molten pool cannot be kept correctly and the molten pool may drop down even in the method of increasing the welding penetration amount of the welding wire in the prior art as mentioned above. Therefore, in the case where the entire attitude welding working of the welding apparatus is required, it is difficult to apply the conventional welding technologies as they are, and as a result in the conventional usual TIG welding method, the welding is performed with a fusing speed of only 10 to 20 g/min for the welding of steel material. That is, in the conventional TIG welding method, although a welded portion with high quality could be obtained, the fusing efficiency was considerably low, so that the application of such TIG welding had a limit in the practical use for the welding of large structures or structures having a large thickness.